1. Field of the Invention
The present invention relates to an apparatus for detecting abnormality of an internal combustion engine-related device and a power output system with such an apparatus. More specifically, the present invention pertains to an apparatus for detecting abnormality of an internal combustion engine-related device, whose state is affected by the driving condition of an internal combustion engine, as well as to a power output system that has such an apparatus and outputs power to a drive shaft.
2. Description of the Related Art
A proposed abnormality detection apparatus for an internal combustion engine-related device detects deterioration of a catalyst packed in a catalytic converter for converting a gaseous exhaust discharged from an internal combustion engine (for example, JAPANESE PATENT LAYING-OPEN GAZETTE No. 5-248227). In this apparatus, deterioration of the catalyst is detected in the following manner. When the internal combustion engine has reached a predetermined driving condition that enables detection of deterioration of the catalyst, the amount of fuel injection is alternately increased and decreased at every 0.5 seconds by 4 to 10% around the mean value in this state. After the start of the inverted variation, signals measured by oxygen sensors disposed before and after the catalytic converter in an air exhaust conduit are respectively plotted for a predetermined time period. The apparatus then accumulates the areas of the oxygen-rich state of the respective plotted sensor signals (the time of the oxygen-rich state in the case of binary signals) and calculates a difference between the respective total areas. When the difference is not less than a predetermined value, it is determined that the catalyst has not deteriorated yet. When the difference is less than the predetermined value, on the other hand, it is determined that the catalyst has deteriorated.
This proposed apparatus, however, has a problem, that is, a difficulty in accurate detection of deterioration of the catalyst. In order to detect deterioration of the catalyst with high accuracy, the internal combustion engine should be kept under the predetermined driving condition for at least a predetermined time period. The driving condition of the internal combustion engine mounted on the vehicle is, however, varied by an instruction of the driver, so that it is rare that the internal combustion engine keeps the same driving condition for the predetermined or longer time period. Even when the internal combustion engine can be kept under the same driving condition for the predetermined or longer time period, the driving condition may be not suitable for detecting deterioration of the catalyst. In order to realize accurate detection of deterioration of the catalyst, detection is carried out only when the internal combustion engine is under the driving condition that is suitable for detecting deterioration of the catalyst. This results in a low frequency of detection and may cause the deteriorating catalyst to be not detected for a relatively long time. An increased frequency of detection for the purpose of avoiding such a problem causes detection to be carried out even when the internal combustion engine is not under the suitable driving condition. This lowers the accuracy of detection and may result in a wrong detection of deterioration of the catalyst.
The above problem arising in the process of detecting abnormality when the internal combustion engine is kept under the predetermined driving condition for the predetermined or longer time period is not restricted to detection of the deteriorating catalyst packed in the catalytic converter, but is also found in any apparatus, whose state is varied by the driving condition of the internal combustion engine.